Electric rotating machine

ABSTRACT

A small, round synchronous motor including a permanent magnet rotor and only a single salient stator pole in magnetic flux relationship with the rotor. Upon the energization of the field coil for the motor, at any given moment the stator pole is of one polarity. When the field coil is de-energized, the rotor consistently assumes a position with respect to the stator pole in which the rotor poles are displaced from the center of the stator pole so that, when the coil is again energized, the rotor is self-starting.

Nov. 6, 1973 United States Patent 11 1 Haydon et a1.

3,495,111 2/1970 Haydon........................... 310/164 X 1 ELECTRICROTATING MACHINE Inventors: Arthur W. Haydon, Middlebury;

Primary Examiner-J. D. Miller Assistant Examiner-H. HuberfeldAttorney-Lee C. Robinson, Jr.

Aug. 25, 1972 [57] ABSTRACT A small, round synchronous motor including aperma- 52 us. 310/156 310/164 310/254 magne and only Mingle Salient Slawin magnetic flux relationship with the rotor. Upon the energization ofthe field coil for the motor, at any given moment the stator pole is ofone polarity. When the field coil is de-energized, the rotorconsistently assumes [51] Int. Cl. H02k 21/16 [58] Field ofSearch.................... 310/152, 156, 162, 310/164,180, 254, 257;318/165, 166

a position with respect to the stator pole in which the rotor poles aredisplaced from the center of the stator [56] References Cited UNITEDSTATES PATENTS pole so that, when the coil is again energized, the rotoris self-starting.

3,014,141 12/1961 Riggs 310/164 X 3,495,107 2/1970Haydon........................... 310/164 X 16 Claims, 11 DrawingFigures PAIENTEDuuv ems 3.770.898

' I SHEETlBFZ BACKGROUND OF THE INVENTION The present invention relatesto electric rotating machines and is particularly applicable toself-starting synchronous motors.

There has been developed an electric motor which exhibits substantialoutput torque at the rotor shaft and is highly efficient. Representativemotors of this type are disclosed, for example, in A. W. Haydon U.S.Pat. No. 3,495,] 13 granted Feb. 10, 1970. Such motors utilize two ormore pole pieces which each have a single stator pole, with the resultthat the motor has a minimum of two such poles. The rotor is reliablyand consistently self-starting, and particularly in cases in whichcertain of the stator poles are shaded the rotor uniformly starts in apredetermined direction.

One problem which has existed in the design of alternating currentmotors and other electric rotating machines, including those of theforegoing type, is that for many appications the unidirectional featureof the rotor is not necessary and only adds to the machinesmanufacturing cost and complexity. However, previous attempts tosimplify the prior machines by eliminating this feature in manyinstances resulted in a motor which was not reliably self-starting. Toretain the self-starting characteristic and for other reasons, it washeretofore generally believed to be necessary to utilize a plurality ofsalient stator poles, often of different instantaneous polarity, inmagnetic flux relationship with the rotor.

SUMMARY OF THE INVENTION One general object of this invention,therefore, is to provide a new and improved electric motor or otherelectric rotating machine.

More specifically, it is an object of this invention to provide amachine of the character indicated which is self-starting and which hasgood starting-and running torque.

Another object of this invention is to provide such a machine of adesign which eliminates certain parts heretofore generally believed tobe necessary.

A further object of this invention is to provide an electric rotatingmachine utilizing comparatively simple mechanical and electricalcomponents which is economical to manufacture and thoroughly reliable inoperation.

In contrast to the prior machines, the foregoing objects are achievedthrough the use of a machine which includes only a single salient statorpole in magnetic flux relationship with the rotor. The stator pole isenergized with an alternating magnetic field, and, at a given moment, isof one polarity. When the machine is deenergized, the rotor consistentlyassumes a position with respect to the stator pole in which the rotorpoles are displaced from the center of the stator pole so that, when themachine is again energized, the rotor is selfstarting. In the quiescentposition of the rotor, the path of minimum reluctance of the magneticflux is one in I which the flux passes from a given rotor pole,circumferentially through the stator pole, and back to another rotorpole.

' The machines of the present invention enable a substantial improvementin economy of design while attaining excellent reliability of startingand operating characteristics. The machines represent such a departurefrom the principle which had been accepted in the prior art that theyconstitute a major breakthrough in the art.

The foregoing and other objects, features and advantages of theinvention will be more readily understood from the following descriptionof certain preferred embodiments, when read with reference to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an exploded perspective viewof an a.c. synchronous motor in accordance with one illustrativeembodiment of the invention.

FIG. 2 is a perspective view of the motor illustrated in FIG. 1 with aportion of the motor housing shown broken away.

FIG. 3 is a fragmentary sectional view taken along line 3-3 in FIG. 2.

FIG. 4 is a schematic sectional view of the relative positions of therotor and the stator pole for the motor when the rotor is in itsquiescent stopping position.

FIG. 5 is a fragmentary side elevational view of an a.c. synchronousmotor in accordance with another illustrative embodiment of theinvention.

FIGS. 6 and 7 are schematic sectional views respectively taken along thelines 66 and 7-7 in FIG. 5 and showing one of the quiescent stoppingpositions for the motor of that figure.

FIGS. 8 and 9 are schematic sectional views respectively similar toFIGS. 6 and 7 but showing another of the quiescent stopping positionsfor the motor of FIG. 5.

FIGS. 10 and 11 are schematic sectional views respectively similar toFIGS. 6 and 7 but showing still another of the quiescent stoppingpositions for the motor of FIG. 5.

DESCRIPTION OF CERTAIN PREFERRE EMBODIMENTS the the leads 25 and 26 fromthe field coil 16 The field coil is wound in conventional fashion on asupporting bobbin 28.

Both the housing 15 and the pole piece 17 are of magnetic material, suchas cold rolled steel, which has high permeability, so as to form lowreluctance magnetic flux paths. The pole piece 17 is in the form of acomparatively shallow cup and, as best shown in FIG. 3, is arranged tofit within the open end of the housing 15. The cylindrical rim portion30 of thee pole piece is in facing contact with the correspondingportion 31 of the housing.

The single salient stator pole 18 is bent at right angles from theclosed end 32 of the pole piece 17, such that the pole piece extends inan axial direction in magnetic flux relationship with the rotor 19. Anopening 33 is provided in the end 32 to accommodate the rotor 19, andthe pole l8 protrudes from the periphery of this opening. The pole 18 isintegral with the remainder of the pole piece 17 to form a continuousmagnetic flux path between the pole piece and the rim portion 30.

The inner end of the pole 18 is spaced in close juxtaposition with theclosed end 23 of the housing 15 to define a small air gap therebetween.

The rotor 19 comprises a comparatively long, thin cylinder of ceramicmagnetic material which is magnetized permanently with but a single pairof opposite north and south poles, as indicated by the letters N and Sin FIG. 4. The rotor material is relatively hard to provide highcoercivity, low permeability, a high magnetic energy product and a lowspecific gravity. Representative examples of such materials areCeramagnet A, A19 and A70 manufactured by Stackpole Carbon Company,Electronic Components Division, St. Marys, Pa., and Index I and Indox Vmanufactured by Indiana General Corporation, Valparaiso, Ind. These areof barium ferrite having a composition of BaFe O Another suitablematerial is Plastiform available from the Leyman Division of MinnesotaMining and Manufacturing Company, Cincinnati, Ohio. The rotor also maybe fabricated from a 77 percent platinum 23 percent cobalt material madeby the Hamilton Watch Company of Lancaster, Pa. This latter material hasa residual induction of 6,400 gauss, a coercive force of 4,300 oerstedsand a maximum energy product of 9.0 X gauss-oersteds. Anotherparticularly advantageous rotor material having an even higher energyproduct is samarium cobalt, also commercially available at the presenttime.

The rotor 19 is provided with an axial hole into which a shaft 35 may besecured as by cementing, moulding or other suitable techniques. Theshaft 35 is rotatably supported between the gear box 20 and a bearing 36which is centrally located within the end 32 of the pole piece 17.Appropriate reduction gearing within the gear box serves to connect theshaft to the output pinion 21. In some cases, particularly wherePlastiform is used as the rotor material, a series of comparatively thinwashers of the material are placed in stacked relationship with eachother on the shaft 35 and are adhesively held together to form therotor. In other preferred embodiments, the Plastiform material may beextruded in tubular form, cut to length and pressed on the shaft.

The use of a long rotor increases the torque available to operate themotor. A relatively high torque is produced when the ratio of rotorlength to diameter exceeds about 1.25 to 1. It appears that a ratio of 3to 1 is particularly suitable. The net usable torque falls off markedlywhen this ratio approaches 1 to 1. In addition, by maintaining the ratioat least about 1.25 to 1 the low inertia of the rotor enablessubstantially instantaneous starting and stopping. This latter featureis particularly advantageous in cases in which the motor is used forintermittent timing operations or for other applications where it isdesired to avoid the introduction of a cumulative error in the positionof the rotor shaft after repeated starts and stops.

FIG. 4 illustrates the relative positions of the rotor 19 and the statorpole 18 with no voltage applied to the field coil. The magnetic poles Nand S of the rotor are each displaced 90 degrees from the center of thestator pole. This represents the quiescent position of minimumreluctance which the rotor will always seek and assume when field poweris interrupted. For rotors which employ multiple pairs of poles, thedisplacement angle 'of the poles in the quiescent position may beexpressed as 90 electrical degrees, 180 electrical degrees being takenas the angular distance from a given rotor pole to an adjacent rotorpole of opposite polarity.

The rotor 19 stops in the quiescent or de-energized position with itstwo poles uniformly centered on opposite sides of the stator pole. Animportant advantage of this quiescent position is that when the statoris again energized, the motor is self-starting. Furthermore, thequiescent rotor position is an exceptionally good one from thestandpoint of producing high starting torque.

To cause the rotor to assume this quiescent position, the stator androtor are so constructed that, when no current is flowing through thefield coil, the reluctance of the magnetic path from the rotor polecircumferentially across the stator pole to the other rotor pole is lessthan the reluctance of the magnetic path from one rotor pole to thestator pole, and then through the stator pole piece to the other rotorpole.

In the embodiment of the invention illustrated in FIGS. 1-4, the angle 0subtended by the stator pole 18 with respect to the rotational axis ofthe rotor 19 is approximately 96.5 mechanical and electrical degrees. Toachieve extremely reliable starting characteristics, the angle subtendedby the stator pole preferable should be maintained within the range offrom about electrical degrees to about electrical degrees. Although angles outside this range may be used for some applications, in cases inwhich the reliable self-starting features of the motor are desired therange should be maintained to prevent the rotor from occasionallyfailing to begin its rotation when the field coil is energized.

When the input leads 25 and 26 (FIG. 1) are supplied with ac. voltage,the pole piece 17 and the stator pole 18 are energized with alternatingmagnetic flux. Because of the unique design of the device, the rotor 19automatically and almost instantaneously begins to rotate from theposition illustrated in FIG. 4 and reaches synchronous speed within thefirst half cycle of the applied wave form. At any given moment duringthe operation of the motor, the stator pole 18 is of one polarity. Thedirection of rotation is determined by the polarity of the first halfcycle. If the fiux from the stator pole is of north (N) polarity, therotor 19 will rotate in a counterclockwise direction, as viewed in FIG.4. If,on the other hand, the flux from the stator pole is of south (S)polarity, the direction of rotation will be clockwise.

In cases in which unidirectional rotation is desired, any of severalconventional mechanical no-back devices may be employed, such as thoseof the camming type, the friction-operated pall type or the ball type.One illustrative device for this purpose is disclosed in Haydon U.S.Pat. No. 3,495,] 13 referred to above. Alternatively, variousnonmechanical arrangements may be utilized to assure unidirectionalrotation.

In addition, in some applications where unidirectional operation may beneeded, a mechanical device of known type may be interposed between themotor and the load to provide a unidirectional drive. As an i1-lustration, the bidirectional characteristics of the rotor may beconverted to oscillating motion which, with a suitable rachet mechanism,may in turn be converted to unidirectional motion.

As the rotor 19 rotates, the flux changes between successive magneticpaths. When the applied voltage approaches the end of the first halfcycle and the stator coil flux approaches zero, the rotor has movedthrough an angle of about 180 from the position shown in FIG. 4. Therotor flux follows a path which passes from the north pole of the rotorto the stator pole 18, circumferentially through the stator pole, backto the south pole of the rotor, and then through the rotor to the northpole. One quarter of an a.c. cycle thereafter, assuming counterclockwiserotation, the north pole of the rotor is opposite the stator pole, andthere is a flux path from the north rotor pole to the stator pole,longitudinally along the stator pole and through the stator structure,back to the south rotor pole and through the rotor to the original pole.Still later, the rotor poles again straddle the stator pole in themanner shown in FIG. 4, and the rotor flux follows a path from the northrotor pole, circumferentially through the stator pole but in theopposite direction from that of the first-mentioned flux, then to thesouth rotor pole and through the rotor to the north pole. One quarter ofa cycle later, the south rotor pole is in line with the stator pole, andthe flux path again extends longitudinally along the stator pole, but inthe opposite direction.

Hence, during operation of the motor, there are four flux condition, theflux tending to switch conditions, succession through these fourconditions. In two of these conditions there is a significant fluxcomponent running circumferentially through the stator pole (clockwiseor counterclockwise, as viewed in FIG. 4). In the other two conditions,the flux in the stator pole is predominantly in a longitudinaldirection.

When the field coil 16 is de-energized, the rotor 19 consistently stopsin a position in which the two rotor poles straddle the stator pole.This is the position of minimum reluctance described heretofore, and thepath of the rotor flux is one in which the flux passes from the northpole of the rotor, circumferentially through the stator pole, back tothe south rotor pole and then through the rotor to the north pole.

FIGS. 5-11 are illustrative of a rotor 40 and a single salient statorpole 41 of an a.c. synchronous motor in accordance with anotherpreferred embodiment of the invention. The stator structure of the motoris similar to that described heretofore with respect to the embodimentof FIGS. I-4 and includes a stator pole piece 42 which cooperates with ahousing and field coil (not shown in FIGS. 5-11 but illustrated inFIG. 1) to produce an alternating magnetic flux. With the field coil inits energized condition, at any given moment the stator pole flux is ofpolarity.

The rotor 40 is in the form of two axially spaced rotor sections 44 and45. The sections 44 and 45 are rigidly affixed to the rotor shaft 46 andeach have only a single pair of rotor poles N and S. The sections 44 and45 should have a fixed angular displacement with respect to one anotherwhich is less than I80 electrical degrees and preferably is of the orderof 90 electrical degrees, as best shown in FIGS. 6 and 7. A washer 47 ofcold rolled steel or other magnetic material serves to maintain thesections in spaced relationship with each other.

The rotor 40' has three possible quiescent stopping positions which arerespectively illustrated in FIGS. 6 and 7, FIGS. 8 and 9, and FIGS. 10and 11. In each of these positions the rotor poles of at least one ofthe sections 44 and 45 are displaced from the center of the stator pole41 so that, when the field coil is again energized, the rotor isself-starting. poles on direction The most natural stopping position forthe rotor 40 is that shown in FIGS. 6 and 7. In this position each ofthe poles of the two rotor sections 44 and 45 is displaced from thecenter of the stator pole 41, and the rotor pole of the section 44closest to the stator pole is of a polarity to that of the closest rotorpole of the section 45. This is the stopping position of minimumreluctance. The magnetic rotor flux follows a path from the north poleof the section 45 to the stator pole 41, then spirally in both an axialand circumferential direction along the stator pole to a positionadjacent the rotor section 44, and then from the stator pole to thesouth pole of this latter section.

Upon the energization of the field coil, the first half cycle of fluxfrom the stator pole 41 is of either north or south polarity. With therotor sections 44 and 45 in their FIGS. 6 and 7 positions, if the statorpole flux is north the sections will rotate in a clockwise direction andwill reach synchronous speed within the first half cycle in the mannerdescribed heretofore with respect to the embodiment of FIGS. 1-4.Conversely, if the stator pole is initially of south polarity, the rotorsections will rotate in a counterclockwise direction, again reachingsynchronous speed within the first half cycle.

In some cases, as a result of friction from the rotor shaft, bearings,gear train, etc., the rotor 40 may stop in the position illustrated inFIGS. 8 and 9. In this latter position, the poles of one of the rotorsections 44 or 45 are in line with the center of the stator pole 41,while the poles of the other rotor section are oriented at ninetydegrees with respect to the center of the stator pole. Here again, whenthe stator pole 41 is energized, a definite starting torque is producedto initiate rotation in one direction or the other. If the rotorsections stop with the north pole of the section 44 adjacent the statorpole, for example, when the stator pole becomes energized with northmagnetic flux there will be no starting torque as a result of thesection 44, but a positive torque will act onn the section 45 to driveboth sections in a counterclockwise direction. More generally, as longas the poles of at least one of the sections are displaced from thecenter of the stator pole, a component of the rotor flux movescircumferentially through the stator pole, and the self-startingcharacteristic of the rotor is maintained.

In certain rare instances, the rotor sections 44 and 45 may come to restin the quiescent stopping position illustrated in FIGS. 10 and 11. Inthis latter position the rotor poles of each section are displaced fromthe center of the stator pole 41 and are in a magnetically balancedcondition, that is, the north pole of each section.

is closer to the stator pole than the south pole, and the north pole areequally spaced on opposite sides of the center of the stator pole. Uponenergization of the field coil, the build-up of magnetic flux begins atthe base of the stator pole adjacent the rotor section 44. The fluxfirst influences the section 44 and will attract or repel (depending onthe-polarity) the adjacent rotor pole of that section prior to the timethe flux influences the rotor section 45.-The section 44 is thus movedin one diretion or the other to similarly move the section 45 andunbalance the interacting magnetic forces to produce the desiredrotation.

The washer 47 between the rotor sections 44 and 45 is believed toimprove the flux relationship between the sections and to provide evenfurther reliability with respect to the self-starting characteristics ofthe motor. In some embodiments of the invention, however, the washer maybe eliminated and the rotor sections placed in abutting relationshipwith each other without materially detracting from the motors operatingparameters.

Each of the motors in accordance with the illustrated embodiments of theinvention is of round configuration and includes an elongated rotorhaving one or more pairs of nonsalient rotor poles of alternatepolarity. The

motors also include only a single unshaded salient stabination:

tor pole in magnetic flux relationship with the rotor. The motorsexhibit high torque and cool running characteristics and are readilysealable in compact units.

Whereas the invention has been described and illustrated with respect toelectric motors, the illustrated and other embodiments may be operatedas alternating current generators. By mechanically driving the rotorshaft, an alternating voltage is produced at the coil leads 2S and 26.

The invention also may be operated as a two-wire or three-wire steppermotor. To provide a two-wire stepper motor, a permanent biasing magnetof the type disclosed in A.W. Haydon US. Pat. No. 3,495,107, forexample, is placed in juxtaposition with the pole piece 17 to bias thestator pole 18 with flux of either north or south polarity. Upon theapplication of unipolar d.c. pulses of the opposite polarity to thefield coil 16, the biasing flux is overcome, and the rotor 19 moves insuccessive discrete increments or steps. For a three-wire stepper motor,the coil 16 is replaced by a split coil having three input leads.

In cases in which it is desired to provide the motor withuni-directional starting characteristics, the permanent biasing magnetmay be employed in combination with a tapered or nonuniform air gapbetween the stator pole 18 and the rotor 19. If, for example, the statorpole 18 is twisted slightly in a clockwise direction from the positionshown in H6. 4, the air gap will be smaller at the right-hand edge ofthe stator pole than at the lefthand edge. If the stator pole isprovided with a south magnetic bias, the quiescent position of the rotor19 will be one in which its north pole faces the right-hand edge of thestator pole. Upon the application of a dc. current pulse to the fieldcoil of a strength and polarity sufficient to produce north magneticflux on the stator pole, the rotor starts in a clockwise direction androtates l80 mechanical degrees. When the pulse terminates, the rotorcontinues its clockwise movement for another 180 mechanical degrees. Therotor thus rotates a full 360 mechanical degrees in response to eachcomplete pulse.

It will be understood from the foregoing that there have been describedself-starting electric rotating machines which employ an entirely novelprinciple of construction and operation and which enable great savingswhile attaining excellent reliability.

The terms and expressions which have been employed are used as terms ofdescription and not of limitation, and there is no intention in the useof such terms and expressions of excluding any equivalents of thefeatures shown and described or portions thereof, but it is recognizedthat various modifications are possible within the scope of theinvention claimed.

What is claimed is:

1. An electric rotating machine comprising, in combination:

a permanent magnet rotor having a plurality of rotor poles of alternatepolarity;

only a single salient stator pole in magnetic flux relationship with therotor; and

a permanent magnet rotor having a plurality of rotor poles of altPrnatealternate only a single salient stator pole in magnetic fluxrelationship with the rotor; and

means for energizing the single salient stator pole with magnetic flux,the rotor being adapted consistently to assume a position with respectto the stator pole, when the machine is in a de-energized condition, inwhich the rotor poles are displaced from the center of the stator poleso that, when the machine is again energized, the rotor is selfstarting.

3. An electric rotating machine as defined in claim 2, in which therotor comprises a plurality of axially spaced rotor sections which eachhave a plurality of rotor poles.

4. An electric rotating machine as defined in claim 3, which furthercomprises magnetic means for maintaining the rotor sections in axiallyspaced relationship.

5. An electric rotating machine comprising, in combination:

a permanent magnet rotor having only a single pair of nonsalient rotorpoles of alternate polarity; only a single salient stator pole inmagnetic flux relationship with the rotor; and

means for energizing the single salient stator pole with magnetic flux,so that at a given moment said stator pole is of one polarity, the rotorbeing adapted consistently to assume a position with respect to thestator pole, when the machine is in a de-energized condition, in whichthe rotor poles are displaced from the center of the stator pole sothat, when the machine is again energized, the rotor is self-starting.

6. A self-starting electric motor comprising, in combination:

a permanent magnet rotor having a plurality of rotor poles of alternatepolarity;

only a single salient stator pole in magnetic flux relationship with therotor, the stator pole being positioned parallel to the axis of rotationof the rotor such that the path of minimum reluctance through the statorpole when the rotor is in its quiescent position is one in which fluxpasses from a given rotor pole, circumferentially through the statorpole, and back to another rotor pole; and

a field coil for energizing the single salient stator pole with magneticflux, the rotor being adapted consistently to assume a position withrespect to the stator pole, when the field coil is de-energized, inwhich the rotor poles are displaced from the center of the stator poleso that, when the field coil is again energized, the rotor isself-starting.

7. A self-starting electric motor as defined in claim 6, in which theangle subtended by the stator pole with respect to the axis of rotationof the rotor is within the range of from about electrical degrees toabout electrical degrees.

8. An electric rotating machine comprising, in combination:

a permanent magnet rotor having nonsalient rotor poles, the ratio of thelength to the diameter of the rotor being at least about 1.25 to 1;

only a single salient stator pole in magnetic flux relationship with therotor, the stator pole being positioned near the rotor poles such thatthe path of minimum reluctance through the stator pole when the rotor isin its quiescent position is one in which fiux passes from a given rotorpole, circumferentially through the stator pole, and back to anotherrotor pole; and

a field coil for energizing the single salient stator pole withalternating magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the field coilis deenergized, in which the rotor poles are displaced from the centerof the stator pole so that, when the field coil is again energized, therotor is selfstarting.

9. An electric rotating machine comprising, in combination:

a permanent magnet rotor having a plurality of nonsalient rotor poles ofalternate polarity;

a cylindrical stator structure coaxial with the rotor,

the stator structure including a stator pole piece of magnetic materialand only a single salient stator pole in magnetic flux relationship withthe rotor; and

means for energizing the single salient stator pole with alternatingmagnetic flux, so that at a given moment said stator pole is of onepolarity, the rotor being adapted consistently to assume a position withrespect to the stator pole, when the machine is in a de-energizedcondition, in which the rotor poles are displaced from the center of thestator pole so that, when the machine is again energized, the rotor isself-starting.

10. An electric rotating machine as defined in claim 9, in which thestator pole piece is of cup-shaped configuration, and the single salientstator pole is integrally formed with the pole piece.

11. An electric rotating machine as defined in claim 9, in which theratio of the length to the diameter of the rotor is at least about 1.25to 1.

12. An electric rotating machine as defined in claim 9, in which therotor is of ceramic material that has high magnetic coercivity, lowpermeability and low specific gravity, the rotor having a greater axiallength than diameter.

13. A self-starting electric motor comprising, in com bination:

a permanent magnet rotor having two rotor pole pairs in axially spacedrelationship with each other; only a single salient pole in magneticflux relationship with the rotor, the stator pole being positioned neareach of the pairs of rotor poles such that the path of minimumreluctance through the stator pole when the rotor is in its quiescentposition is one in which flux passes from a given rotor pole,circumferentially through the stator pole, and back to another rotorpole; and field coil for energizing the single salient pole withalternating magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the field coilis de-energized, in which the rotor poles in at least one of said pairsare displaced from the center of the stator pole so that, when the fieldcoil is again energized, the rotor is self-starting.

14. A self-starting electric motor comprising, in combination:

a permanent magnet rotor having nonsalient rotor pole pairs in axiallyspaced relationship with each other, the respective pairs having a fixedangular displacement with respect to one another which is less thanelectrical degrees;

only a single salient stator pole in magnetic flux relationship with therotor, the stator pole being positioned near each of the pairs of rotorpoles such that the path of minimum reluctance through the stator polewhen the rotor is in its quiescent position is one in which flux passesfrom a given rotor pole, circumferentially through the stator pole, andback to another rotor pole; and

a field coil for energizing the single salient stator pole withalternating magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the field coilis deenergized, in which the rotor poles in at least one of said pairsare displaced from the center of the stator pole so that, when the fieldcoil is again energized, the rotor is self-starting.

15. A self-starting electric motor comprising, in combination:

a permanent magnet rotor including two axially spaced rotor sectionswhich each having only a single pair of nonsalient rotor poles, therotor pole pairs in the respective sections having a fixed angulardisplacement with respect to one another;

only a single salient stator pole in magnetic flux relationship with therotor; and

a field coil for energizing the single salient stator pole withalternating magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the field coilis deenergized, in which the rotor poles in at least one of said pairsare displaced from the center of the stator pole so that, when the fieldcoil is again energized, the rotor is self-starting.

16. A self-starting electric motor comprising, in combination:

a rotor including two permanent magnet rotor sections and anintermediate section of magnetic material for maintaining the permanentmagnet sections in axially spaced relationship with each other, each ofthe permanent magnet section having a pair of nonsalient rotor polesarranged such that the rotor poles in the respective sections have afixed angular displacement with respect to one another which is lessthan 180 electrical degrees;

only a single salient stator pole in magnetic flux relationship with therotor, the stator pole being positioned near each of the pairs of rotorpoles such that the pathof minimum reluctance through the stator polewhen the rotor is in its quiescent position is one in which flux passesfrom a given rotor pole, circumferentially through the stator pole, andback to another rotor pole; and

a field coil for energizing the single salient stator pole withalternating magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the field coilis deenergized, in which the rotor poles in at least one of said pairsare displaced from the center of the stator pole so that, when the fieldcoil is again energized, the rotor is self-starting. a :r

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 7 ,998Dated November 6, 1973,

Inventofl Arthur W; Havdon It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

Column l,' last line "principle" should be plural. Column line 37, "the"should be deleted.

Column line 56, "thee" should be changed to the--. Column 5, line 46,"one" should be inserted after "of".

' Column 5,; ;l ine 63 "poles on direction"' should be deleted.

Column 6,- line 2, --oppositeshould be inserted after "polarity".

Column-6, line 35, "onn" 'should be changed to --on--.

Column 8, .line 7, "altPrnate alternate" should be changed to -alternatepo1arity;--.

Signedband sealed this 27th day of August 1974.

@- .EALl.

a test:

MCCOY M. GIBSON", JR. T c. MARSHALL. DANN Attesting Officer I ICOIIIIIIIS'SIOIIG'I of Patents FORM Po-1050 (10-69) I I USCOMM-DC6O376-I=69 ILS. GOVERNMENT PRINTING OFFICE 1 I'll O-lil-JS.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 7 ,998Dated November 6, 1973 Invent0 Arthur W4 Havdon It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column last line "principle" should be plural.

Column 2, line 37, "the" should be deleted.

Column line 56, "thee" should be changed to the-. Column 5, line 46,"one" should be inserted after "of". Column 5,,line 63, "pol es ondirection" should be deleted Column 6, line 2, --opposite-- should beinserted after "polarity".

Column 6, 7 line 35, "onn" Should be changed to --on.

Column 8, line 7, "altPrnate alternate", should be changed to--alternate polarity;---;

Signed and sealed this 27th day of August 1974.

(SEAL), lk ctestz' V COY M. GIBSON" JR. C. MARSELALL DANN lfitestingOifiee'r' COTHIIliSSlOIlGT of Patents FORM PO-1050 (10-69) Y 7 USCOMM DC6037645" 1:: u.sv aovnunzm ram-nus omc: no o-su-au. i

1. An electric rotating machine comprising, in combination: a permanentmagnet rotor having a plurality of rotor poles of alternate polarity;only a single salient stator pole in magnetic flux relationship with therotor; and means for energizing the single salient stator pole withmagnetic flux, so that at a given moment said stator pole is of onepolarity.
 2. An electric rotating machine comprising, in combination: apermanent magnet rotor having a plurality of rotor poles of altPrnatealternate only a single salient stator pole in magnetic fluxrelationship with the rotor; and means for energizing the single salientstator pole with magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the machine isin a de-energized condition, in which the rotor poles are displaced fromthe center of the stator pole so that, when the machine is againenergized, the rotor is self-starting.
 3. An electric rotating machineas defined in claim 2, in which the rotor comprises a plurality ofaxially spaced rotor sections which each have a plurality of rotorpoles.
 4. An electric rotating machine as defined in claim 3, whichfurther comprises magnetic means for maintaining the rotor sections inaxially spaced relationship.
 5. An electric rotating machine comprising,in combination: a permanent magnet rotor having only a single pair ofnonsalient rotor poles of alternate polarity; only a single salientstator pole in magnetic flux relationship with the rotor; and means forenergizing the single salient stator pole with magnetic flux, so that ata given moment said stator pole is of one polarity, the rotor beingadapted consistently to assume a position with respect to the statorpole, when the machine is in a de-energized condition, in which therotor poles are displaced from the center of the stator pole so that,when the machine is again energized, the rotor is self-starting.
 6. Aself-starting electric motor comprising, in combination: a permanentmagnet rotor having a plurality of rotor poles of alternate polarity;only a single salient stator pole in magnetic flux relationship with therotor, the stator pole being positioned parallel to the axis of rotationof the rotor such that the path of minimum reluctance through the statorpole when the rotor is in its quiescent position is one in which fluxpasses from a given rotor pole, circumferentially through the statorpole, and back to another rotor pole; and a field coil for energizingthe single salient stator pole with magnetic flux, the rotor beingadapted consistently to assume a position with respect to the statorpole, when the field coil is de-energized, in which the rotor poles aredisPlaced from the center of the stator pole so that, when the fieldcoil is again energized, the rotor is self-starting.
 7. A self-startingelectric motor as defined in claim 6, in which the angle subtended bythe stator pole with respect to the axis of rotation of the rotor iswithin the range of from about 90 electrical degrees to about 180electrical degrees.
 8. An electric rotating machine comprising, incombination: a permanent magnet rotor having nonsalient rotor poles, theratio of the length to the diameter of the rotor being at least about1.25 to 1; only a single salient stator pole in magnetic fluxrelationship with the rotor, the stator pole being positioned near therotor poles such that the path of minimum reluctance through the statorpole when the rotor is in its quiescent position is one in which fluxpasses from a given rotor pole, circumferentially through the statorpole, and back to another rotor pole; and a field coil for energizingthe single salient stator pole with alternating magnetic flux, the rotorbeing adapted consistently to assume a position with respect to thestator pole, when the field coil is de-energized, in which the rotorpoles are displaced from the center of the stator pole so that, when thefield coil is again energized, the rotor is self-starting.
 9. Anelectric rotating machine comprising, in combination: a permanent magnetrotor having a plurality of non-salient rotor poles of alternatepolarity; a cylindrical stator structure coaxial with the rotor, thestator structure including a stator pole piece of magnetic material andonly a single salient stator pole in magnetic flux relationship with therotor; and means for energizing the single salient stator pole withalternating magnetic flux, so that at a given moment said stator pole isof one polarity, the rotor being adapted consistently to assume aposition with respect to the stator pole, when the machine is in ade-energized condition, in which the rotor poles are displaced from thecenter of the stator pole so that, when the machine is again energized,the rotor is self-starting.
 10. An electric rotating machine as definedin claim 9, in which the stator pole piece is of cup-shapedconfiguration, and the single salient stator pole is integrally formedwith the pole piece.
 11. An electric rotating machine as defined inclaim 9, in which the ratio of the length to the diameter of the rotoris at least about 1.25 to
 1. 12. An electric rotating machine as definedin claim 9, in which the rotor is of ceramic material that has highmagnetic coercivity, low permeability and low specific gravity, therotor having a greater axial length than diameter.
 13. A self-startingelectric motor comprising, in combination: a permanent magnet rotorhaving two rotor pole pairs in axially spaced relationship with eachother; only a single salient pole in magnetic flux relationship with therotor, the stator pole being positioned near each of the pairs of rotorpoles such that the path of minimum reluctance through the stator polewhen the rotor is in its quiescent position is one in which flux passesfrom a given rotor pole, circumferentially through the stator pole, andback to another rotor pole; and a field coil for energizing the singlesalient pole with alternating magnetic flux, the rotor being adaptedconsistently to assume a position with respect to the stator pole, whenthe field coil is de-energized, in which the rotor poles in at least oneof said pairs are displaced from the center of the stator pole so that,when the field coil is again energized, the rotor is self-starting. 14.A self-starting electric motor comprising, in combination: a permanentmagnet rotor having nonsalient rotor pole pairs in axially spacedrelationship with each other, the respective pairs having a fixedangular displacement with respect to one another which is less than 180electrical degrees; only a single salient stator pole in magnetic fluxrelationship with the rotor, the stator pole being positioned near eachof the pairs of rotor poles such that the path of minimum reluctancethrough the stator pole when the rotor is in its quiescent position isone in which flux passes from a given rotor pole, circumferentiallythrough the stator pole, and back to another rotor pole; and a fieldcoil for energizing the single salient stator pole with alternatingmagnetic flux, the rotor being adapted consistently to assume a positionwith respect to the stator pole, when the field coil is de-energized, inwhich the rotor poles in at least one of said pairs are displaced fromthe center of the stator pole so that, when the field coil is againenergized, the rotor is self-starting.
 15. A self-starting electricmotor comprising, in combination: a permanent magnet rotor including twoaxially spaced rotor sections which each having only a single pair ofnonsalient rotor poles, the rotor pole pairs in the respective sectionshaving a fixed angular displacement with respect to one another; only asingle salient stator pole in magnetic flux relationship with the rotor;and a field coil for energizing the single salient stator pole withalternating magnetic flux, the rotor being adapted consistently toassume a position with respect to the stator pole, when the field coilis de-energized, in which the rotor poles in at least one of said pairsare displaced from the center of the stator pole so that, when the fieldcoil is again energized, the rotor is self-starting.
 16. A self-startingelectric motor comprising, in combination: a rotor including twopermanent magnet rotor sections and an intermediate section of magneticmaterial for maintaining the permanent magnet sections in axially spacedrelationship with each other, each of the permanent magnet sectionhaving a pair of nonsalient rotor poles arranged such that the rotorpoles in the respective sections have a fixed angular displacement withrespect to one another which is less than 180 electrical degrees; only asingle salient stator pole in magnetic flux relationship with the rotor,the stator pole being positioned near each of the pairs of rotor polessuch that the path of minimum reluctance through the stator pole whenthe rotor is in its quiescent position is one in which flux passes froma given rotor pole, circumferentially through the stator pole, and backto another rotor pole; and a field coil for energizing the singlesalient stator pole with alternating magnetic flux, the rotor beingadapted consistently to assume a position with respect to the statorpole, when the field coil is de-energized, in which the rotor poles inat least one of said pairs are displaced from the center of the statorpole so that, when the field coil is again energized, the rotor isself-starting.